The invention concerns a device for cooling a metal strip between two rolling stands, where the strip is guided over a guide element designed with a flat area, and where a spray element is installed below the guide element and directs cooling medium at the underside of the strip through at least one opening in the guide element.
In hot rolling mills, cooling is used between the rolling stands to control the surface temperature of the strip. Cooling between the stands achieves basically two objectives:
First, it prevents resealing of the strip by applying a small amount of water to the surface of the strip. This mode of operation is used mainly downstream of the first, more slowly running stands.
Second, the strip temperature is adjusted by cooling between the stands as part of the technological process management for adjusting certain material properties by applying the amount of water to the strip that is necessary for this purpose.
In this connection, it is important that the water be applied to the largest possible surface area of the strip. The amounts of water that are typically necessary for cooling between the stands varies from about 80 to 280 m3/h with application of water to both sides of the strip. The water pressure in this operation is 1-10 bars.
To achieve an enhanced cooling effect of the rolling stand with the same length of a cooling zone between two stands, EP 0 998 993 B1 provides a combination of cooling between the stands and an additional roll cooling in the area of the runout side of the roll gap with the use of a directed stream of pressurized water along a circumferential region of the roll barrel of each work roll. In this process, the cooling between rolls and the roll cooling are each carried out with contactless sealing means for the surface of the rolling stock and the surface of the roll barrel.
DE 37 04 599 A1 describes a method for cooling hot rolling stock moving on a horizontal conveyor, where liquid coolant in the form of laminar water curtains is applied to the rolling stock from above and below. To keep the consumption of cooling water low, the cited patent provides that the water curtains can be adjusted in their width and thickness continuously and independently of each other.
EP 1 399 277 B1 discloses a method for cooling and lubricating the rolls of a rolling stand, in which, for the purpose of economical roll cooling and lubrication, either only lubricant is applied, or only the rolling stock cooling system is activated, depending on boundary conditions and requirements.
EP 1 624 078 A1 discloses a device for cooling a strip of sheet metal with nozzles for a cooling liquid to be sprayed onto the underside of the strip arranged below the strip in rows transverse to the direction of strip conveyance. To create favorable cooling conditions, the cited patent provides that the nozzles, which are designed as fan nozzles, form a common central spraying surface for each transversal row. The invention also provides that covers, which are positioned alongside the strip of sheet metal, are provided in the spraying region of the nozzles.
WO 2005/115651 A1 discloses a method and a device for cooling and/or lubricating rolls and/or rolling stock with the use of cooling medium and base oil. To realize improved lubrication in the roll gap, the cooling medium is applied to the rolls separately from the base oil, and exclusively the base oil, without water as a carrier medium, is applied directly to the rolling stock over its entire width in an amount that is very small relative to the usual amount.
EP 1 527 829 A1 and JP 2002-239623 A describe solutions in which cooling devices have a guide element in which a pattern of holes is incorporated to ensure the admission of cooling liquid to the strip to be cooled.
In cooling systems between rolling stands, a specific problem that arises is that both at minimum pressure and at maximum pressure, it is necessary to achieve a spray pattern of the cooling liquid on the strip to be cooled that ensures overlapping that is sufficient to avoid roping on the surface of the strip.
In this regard, special attention must be paid to the spray pattern produced at the lower nozzle spray bar, i.e., during the spraying of the strip with a nozzle spray bar on the underside of the strip. The lower nozzle spray bar is located below a guide table, on which the strip to be cooled is running. The guide table has especially the job of guiding the strip horizontally between an outlet guide and a looper.
The spray water of the lower nozzle spray bar must be conveyed through the guide table. This means that the guide table must be provided with openings for the cooling medium. In this regard, it has been found that the formation of unspecifically shaped openings does not lead to a satisfactory result. Optimal spray patterns cannot be realized without specific shaping of the openings. In addition, in the case of unspecifically shaped openings, unacceptable mechanical weakening of the guide table can occur.